Motor vehicle gearbox

ABSTRACT

Motor vehicle gearbox with two concentrically mounted input shafts ( 6, 9 ), each driving an individual layshaft ( 12, 15 ), having gears ( 16 - 19, 41 ) in engagement with gears ( 21, 22, 40 ) on an output shaft. One layshaft ( 12 ) has a central synchronization device ( 30 ), by means of which the layshaft which is driveably coupled to the momentarily non-driven input shaft, can be accelerated up to a rotational speed chosen by the selected gear speed. The central synchronization device ( 30 ) has a friction clutch ( 34 ) and two synchronization gears ( 32, 33 ) of different diameter, the gear ( 33 ) of smaller diameter being widened relative to the other and being lockable to the shaft ( 12 ) by means of an engagement sleeve ( 63 ), so that drive torque can be transmitted via the synchronization gear ( 33 ). The second layshaft ( 15 ) is releasable by means of an engagement device ( 55 ), whereby torque can be transmitted from one layshaft ( 12 ) to the other ( 15 ) and to the output shaft ( 20 ), which results in a faster reverse gear than the ordinary reverse gear.

[0001] The present invention relates to a motor vehicle gearbox,comprising at least two concentrically arranged alternately driveablefirst and second input shafts, first and second layshafts, primary gearscarried by the first input shaft and the first layshaft, said primarygears engaging each other for transmitting torque from the first inputshaft to the first layshaft, primary gears carried by the second inputshaft and the second layshaft, said primary gears engaging each otherfor transmitting torque from the second input shaft to the secondlayshaft, an output shaft, gears carried by the layshafts and the outputshaft, said gears engaged in each other in pairs for transmitting torquefrom either layshaft to the output shaft and of which at least one gearin each pair is a releasable idle gear, and synchronizing meanscomprising firstly a pair of synchronizing gears of different diametersrotatably mounted on one of the layshafts, said gears being in drivingengagement with gear rings on one input shaft, and secondly frictionmeans, by means of which a driving connection between one synchronizinggear and the shaft can be established to adapt the rotational speed ofthe layshaft which is driveably coupled to the momentarily undriveninput shaft, to a rotational speed determined by the selected gearspeed, at least the synchronizing gear of smaller diameter beingcoordinated with engaging means which permits transmission of highertorque to its layshaft than what is required for said rotational speedadaption.

[0002] A gearbox of the above stated type is previously known fromSE-A-507 366. It is based on a so-called “power-shift” gearbox with atwo-position central synchronization, whereby six synchronizingfunctions are obtained in a seven-speed gearbox with two synchronizinggears and a synchronizing clutch on one of the layshafts. It is furtherdeveloped in that one of the synchronizing gears is made so that it canalso be used for torque transmission to provide an additional gearspeed, namely an overdrive. Practically, this can be achieved bywidening one of the normally quite narrow synchronization gears andproviding it with engaging means which provides a shape engagementinstead of a friction engagement. The purpose of the present inventionis, in a gearbox of the type described by way of introduction, toincrease the number of gear ratios with the smallest possible economicinvestment and design work.

[0003] This is achieved according to the invention by virtue of the factthat that the primary gear of the second layshaft is coordinated withengaging means, whereby the primary gear is releasable from and lockableto its shaft, and that the primary gear is releasable from its shaft atthe same time as the synchronizing gear of smaller diameter is lockableby means of its engagement means to its shaft to permit torquetransmission from the second input shaft via said synchronization gearand inter-engaging gears on the first and second layshafts to the outputshaft.

[0004] Merely by arranging the primary gear of the second layshaft to bereleasable, which is known per se in other contexts, and coordinatingthis release with the engagement of the other synchronization gear, i.e.the overdrive gear, a second reverse gear is obtained with a lower gearratio than the existing reverse gear. To do such design work, only oneadditional engaging means is required to provide the gearbox the gearboxshown in SE-A-507 366 with an additional gear speed.

[0005] The invention will be described in more detail with reference toan example shown in the accompanying drawing, where the FIGURE shows alongitudinal section through a gearbox with seven regular gears plusoverdrive and reverse gear.

[0006]1 in the Figures designates an engine fly wheel, which via amulti-disk wet disk clutch, generally designated 2, drives a gearbox 3according to the invention. The clutch 2 is a double clutch of a typeknown per se and therefore it does not need to be described in moredetail here. The left hand clutch unit 4 seen in the FIGURE is coupledvia a sleeve element 5 to a first input shaft 6 in the gearbox, whilethe right hand clutch unit 7 is coupled via a sleeve element 8 to asecond input shaft 9 in the form of a hollow shaft mountedconcentrically with the first shaft 6. The two clutch units can bealternately engaged and disengaged to alternately drive the input shafts6 and 9. The wet disk clutch shown can be replaced by a double dry diskclutch.

[0007] The first input shaft 6 is provided with a gear ring 10, inengagement with a gear 111 which is solidly mounted on a first layshaft12. The second input shaft 9 is made with a gear ring 13 which is inengagement with a gear 14 which is mounted on a second layshaft 15. Thegear ring 13 is larger than the gear ring 10, which means that thesecond layshaft 15 will rotate more rapidly than the first layshaft 12at the same input rpm for the respective input shaft.

[0008] The layshafts 12 and 15 respectively each support a pair offreely rotatably mounted gears 16, 17 and 18, 19 respectively, of whichthe gears 16, 18 are both in engagement with a gear 21 fixedly mountedon the output shaft 20, and the gears 17, 19 are in engagement with agear 22 which is rotatably mounted on the output shaft and can be lockedto the shaft with the aid of an engaging sleeve 27. The shafts arearranged in a V shape in order to make it possible, with the aid of anextra gear 23 on the layshaft 15, said gear engaging the gear 11 on thelayshaft 12, to reverse the rotational direction of one of the layshaftsfor proviging a reverse gear. It is also possible to reverse therotational direction of the respective layshaft by means of a gearmounted on a separate shaft in the housing, said gear engaging the gearrings 10 and 23. This provides a freer selection of V shape and gearratios and also permits the shafts to be placed in the same plane. Thegears 16, 17, 18, 19 and 23 are lockable to their shafts with the aid ofaxially displaceable engaging sleeves 24, 25 and 26. A gear 40 freelyrotatably mounted on the output shaft 20 engages the gear ring 41integral with the layshaft 15 and is lockable to the shaft 20 by meansof an engaging sleeve 42. By cutting the gear ring 41 directly in thelayshaft 15 and arranging the gear 40 lockable to the output shaft, theneed for needle bearings on the layshaft is eliminated and the gear canbe made with a very small diameter, which in turn provides a higher gearratio from the layshaft to the output shaft. With the aid of theengaging sleeve 27, the input shaft 6 and the output shaft 20 can belocked together for direct drive. All of these engaging sleeves arewithout individual, conventional synchronizing devices.

[0009] The first layshaft 12 is instead co-ordinated with a centralsynchronizing device generally designated 30. It comprises a pair ofgears 32, 33 freely rotatably mounted on an extension 31 of the layshaft12 with a clutch disk 34 therebetween. The clutch disk 34 is axiallydisplaceable but non rotatably mounted relative to the shaft 12 by meansof splines. The clutch disk is joined to operating means, not shown inmore detail here, for controlling the shifting. The synchronizing gears32, 33 have on their sides facing the disk 34 frictional surfaces 37,38. The left hand gear 32 engages a gear ring 39 on the second inputshaft 9. The gear ring 39 has a smaller diameter than the gear ring 10on the first input shaft. The right hand synchronizing gear 33 engagesthe gear ring 13 on the second input shaft and here there is preferablya difference of one or two gear teeth between the synchronizing gear 33and the driven gear 14 on the second layshaft.

[0010] For more detailed description of the synchronizing sequencereference is made to SE-A-507 366.

[0011] In order to be able to utilize the synchronizing gear 33 fortorque transmission it has been widened relative to the gear 32 andcoordinated with an engagement device 60 which provides a shape-boundengagement. The engagement device 60 comprises a hub 61 solidly joinedto the layshaft 12. The hub 61 has external splines 62 which engagecorresponding internal splines on the engagement sleeve 63. The gear 33is provided with a ring of splines 64.

[0012] When torque is to be transmitted via the synchronization gear 33the gear is locked to the shaft by axial displacement of the engagementsleeve 63, so that its splines engage with the splines 64 of the gear33. The torque is now transmitted as indicated by the dash-dot OD linein the FIGURE, thereby providing an additional gear speed, an overdrive,which has a higher rpm on the output shaft 20 than on the input shaft 6.

[0013] According to the invention the primary gear 14 of the secondlayshaft is freely rotatably mounted on the shaft and is coordinatedwith an engagement device 55 which comprises a hub 56, non-rotatablyjoined to the layshaft 15. The hub has external splines 57 which engagecorresponding internal splines on an engagement sleeve 58. The gear 14is made with a ring of splines 59.

[0014] With the gear 33 locked on the layshaft 12 and gear 14 releasedfrom the layshaft 15, torque can be transmitted from the layshaft 12 tothe layshaft 15 and from there to the output shaft 20, as marked withthe line R2 in the FIGURE, thus providing a faster reverse gear, i.e. areverse gear with a lower gear ratio than the ordinary reverse gear. Thetorque path for the ordinary reverse gear is marked with the line R1 inthe FIGURE.

1. motor vehicle gearbox, comprising at least two concentricallyarranged alternately driveable first and second input shafts (6,9),first and second layshafts (12,15), primary gears carried by the firstinput shaft (6) and the first layshaft (12), said primary gears (10,11)engaging each other for transmitting torque from the first input shaft(6) to the first layshaft (12), primary gears (13,14) carried by thesecond input shaft (9) and the second layshaft (15), said primary gearsengaging each other for transmitting torque from the second input shaft(9) to the second layshaft (15), an output shaft (20), gears(16,17,18,19,21,22) carried by the layshafts and the output shaft, saidgears engaged in each other in pairs for transmitting torque from eitherlayshaft to the output shaft and of which at least one gear in each pairis a releasable idler gear, and synchronizing means (30) comprisingfirstly a pair of synchronizing gears of different diameters rotatablymounted on one of the layshafts, said gears being in driving engagementwith gear rings (13,39) on one input shaft (9), and secondly frictionmeans (34), by means of which a driving connection between onesynchronizing gear (32,333) and the layshaft (12) can be established toadapt the rotational speed of the layshaft which is driveably coupled tothe momentarily undriven input shaft, to a rotational speed determinedby the selected gear speed, at least the synchronizing gear (33) ofsmaller diameter being coordinated with engaging means (60) whichpermits transmission of higher torque to its layshaft than what isrequired for said rotational speed adaption, characaterized in that theprimary gear (14) of the second layshaft (15) is coordinated withengaging means (55), whereby the primary gear (14) is releasable fromand lockable to its shaft (14), and that the primary gear is releasablefrom its shaft at the same time as the synchronizing gear (33) ofsmaller diameter is lockable, by means of its engagement means (60) toits shaft (12) to permit torque transmission from the second input shaft(9) via said synchronization gear (33) and inter-engaging gears (11,12)on the first and second layshafts (12,15) to the output shaft (20). 2.Gearbox according to claim 1, characterized in that the synchronizationgear (33) of smaller diameter is coordinated with a separate engagementmeans (60), which permits transmission of higher torques to its layshaft(12) than the friction means (34).
 3. Gearbox according to claim 1 or 2,characterized in that the synchronization gear (33) of smaller diameterengages a primary gear (13) arranged on one input shaft (9) and that thegear ratio bewteen these is lower than the gear ratio between theprimary gear (10) of the second input shaft (6) and the primary gear(11) in engagement therewith, on the layshaft (12).
 4. Gearbox accordingto one of claims 1-3, characterized in that synchronization gear (33) ofsmaller diameter has a gear ring of larger axial dimension than the gearring of the second synchronization gear (32).
 5. Gearbox according toone of claims 1-4, characterized in that the engagement means (60)comprise an engaging hub (61) non-rotatably joined to the associatedlayshaft (1), said hub, non-rotatably but axiallly displaceably carriesan engagement sleeve (63) with internal engaging teeth (62), which upondisplacement of the engagement sleeve in one direction are insertableinto engagement with corresponding engagement teeth (64) on thesynchronization gear (33) for locking it to the layshaft (12).